1. Field of the Invention
The present invention relates to a signature-stacking apparatus in which signatures delivered from, for example, a folding unit of a rotary printing press are conveyed to a stacking section by means of a conveyor chain having gripping mechanisms conveys; groups of signatures, each group consisting of a predetermined number of signatures whose creases face the same direction, are stacked in the stacking section such that the direction in which the creases of signatures face alternates from group to group; and the thus-formed stack of signatures is delivered from the apparatus.
2. Description of the Related Art
A conventional signature-stacking apparatus is disclosed in, for example, Japanese Patent No. 2533825.
The disclosed signature-stacking apparatus is configured as follows. Conveying means (hereinafter referred to as a “conveyor chain”) having holding means (hereinafter referred to as “gripping mechanisms”) for gripping corresponding signatures conveys signatures to stacking means (hereinafter referred to as a “stacking section”) for stacking signatures. On the way to the stacking section, the gripping mechanisms in a predetermined number pivotally change their orientation clockwise or counterclockwise by a predetermined angle; for example, 90 degrees. Then, the gripping mechanisms release corresponding signatures one after another, so that the released signatures fall into the stacking section located below the release point. Groups of signatures, each group consisting of a predetermined number of signatures whose creases face the same direction, are stacked such that the direction in which the creases of signatures face alternates from group to group by two times the predetermined angle; for example, by 180 degrees. Thus is formed a stack of signatures.
A gripping mechanism grips a signature at the so-called crease side where a single crease is externally present, since a plurality of leaf ends are arranged in layers at the so-called leaf-end side of the signature and are difficult to grip without one or more leaf ends being left ungripped. Therefore, the signature falls into the stacking section while being led by the leaf-end side.
The signature-stacking apparatus disclosed in Japanese Patent No. 2533825 involves the following problems.
As mentioned above, a signature released from a gripping mechanism falls gravitationally while being led by the leaf-end side. In the course of falling, air resistance may cause leaf ends to fan out or bend, potentially decelerating the falling speed and causing a variation in falling speed. As a result, two adjacently falling signatures may contact each other. Therefore, signatures encounter difficulty in falling in a stable condition and are consequently stacked in a misaligned condition, potentially raising a problem in a later step of working a stack of signatures; for example, in a packing or binding step.
When signatures fall while their leaf ends fan out or bend, and are then stacked, leaves of the stacked signatures may be folded, resulting in impaired quality. Deceleration of falling speed is an obstacle to speeding up a step of working signatures.
In order to change the orientation of signatures, the gripping mechanisms are rotated 90 degrees about the vertical direction and are slid in a direction perpendicular to both the vertical direction and the direction of conveyance. Thus, the conveying means, which is composed of the conveyor chain and the gripping mechanisms, must employ a complicated mechanism for effecting a gripping action and an orientation-changing action. As a result, the possibility of malfunctioning increases. Also, since relatively frequent maintenance is required, running cost increases.